The following descriptions are not admitted to be prior art by virtue of their inclusion in this section.
Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems facilitate increased productivity and cost reduction in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. A number of systems and methods utilize devices communicatively networked together in order to facilitate realization of these beneficial results. However, traditional communication approaches can be susceptible to a number of reliability and/or timing issues.
Conventional video transport networks generally have multiple point-to-point communication links that communicate information from a video source (e.g., cameras, video distribution equipment, production switchers, video routers, video encoders, video decoders and the like) to a video destination (e.g., video monitors, video broadcast equipment, video distribution equipment, production switchers, video routers, video encoders and/or video decoders, etc.). While conventional video transport networks often communicate a significant amount of information, communication failures can result from a variety of causes (e.g., bad cable, bad connectors, poor or no connection, electromagnetic interference, electrostatic discharge, poor signal integrity, and/or high signal attenuation, etc.). Traditional communication links often lack mechanisms to enhance data integrity. For example, if a communication channel fails, typically either no data or erroneous data is received. Moreover, communication links in video broadcast networks are usually unidirectional and there is generally no return path (e.g., between a receiving stage and a previous transmission stage) available to request the original transmitter to retransmit the data in the event of an error. In addition, the temporal nature of live video often makes retransmission impractical.
Traditional attempts at addressing communication errors usually involve delays. In one conventional approach to link error recovery in the broadcast video arts, data is transmitted over two different links to two different line-cards that are located either in the same rack or in two different racks. Conventional Art FIG. 1 illustrates examples of such arrangements. If both links are good, the data from the primary link is fed to the first destination line card through a communication system, which might comprise a backplane of a rack. Whenever there is a bad first link, a link/error monitoring function in the primary line card reports an error signal to the central processing subsystem. The central processing subsystem might be present in the same card, a different card, or a different rack. The central processing subsystem switches to the data received on the alternate second link by the second destination line card.
In addition to utilizing two line cards, such conventional art approaches often involve a relatively significant time delay between a time at which the active line card detects an error and a time at which the second destination line card starts receiving valid data from an alternate link. Traditionally, multiple events generally happen in order for valid data to be successfully recovered and delivered from the alternate link. For example, a primary link line card detects an error condition which is reported to a central processing subsystem. The central processing subsystem sends a stimulus to switch data from the one line card to the other line card. Due to the time required to accomplish this sequence of events, the actual switch-over time is often much longer than desired and/or tolerable. In addition, there is typically significant data loss and/or erroneous data reception.
Conventional art approaches attempting link error recovery in the broadcast video arts sometimes involve transmitting the same data stream in primary and alternate links. Conventional Art FIG. 2 illustrates an example of this arrangement. At the entry point into the two receiving ports, the primary and secondary links are fed to a 2-to-1 multiplexer. The output of the multiplexer is fed into a clock and data recovery unit. The data recovered from the clock and data recovery unit is de-serialized and fed to the video processing blocks. Whenever the link/error monitoring function reports an error, the select line of the multiplexer is toggled to select the alternate link.
This second conventional art method can also involve a number of issues. In addition to the delay between the occurrence of an error condition and changing a multiplexer select line, this system performs the switch in the serial domain. In addition, generally the approach also allows time for a phase locked loop (PLL) to reacquire lock in order to produce a clock signal for data framing. During this interval, the data to the video processor can be erroneous or lost. Furthermore, the traditional systems typically monitor errors on one link and have not determined if a switch to the alternate link is appropriate (e.g., the alternate link has less errors and/or better connections).